dongwei2610
2013-08-15 08:27
浏览 123
已采纳

如何在golang中将数据结构作为参数传递

XML to Json

package main

import (
    "encoding/json"
    "encoding/xml"
    "fmt"
)

type Persons struct {
    Person []struct {
        Name string
        Age  int
    }
}
type Places struct {
    Place []struct {
        Name    string
        Country string
    }
}

type Parks struct {
    Park struct {
        Name     []string
        Capacity []int
    }
}

const personXml = `
    <Persons>
        <Person><Name>Koti</Name><Age>30</Age></Person>
        <Person><Name>Kanna</Name><Age>29</Age></Person>
    </Persons>
`

const placeXml = `
    <Places>
        <Place><Name>Chennai</Name><Country>India</Country></Place>
        <Place><Name>London</Name><Country>UK</Country></Place>
    </Places>
`

const parkXml = `
    <Parks>
        <Park><Name>National Park</Name><Capacity>10000</Capacity></Park>
        <Park>Asian Park</Name><Capacity>20000</Capacity></Park>
    </Parks>
`

func WhatIamUsing() {
    var persons Persons
    xml.Unmarshal([]byte(personXml), &persons)
    per, _ := json.Marshal(persons)
    fmt.Printf("%s
", per)

    var places Places
    xml.Unmarshal([]byte(placeXml), &places)
    pla, _ := json.Marshal(places)
    fmt.Printf("%s
", pla)

    var parks Parks
    xml.Unmarshal([]byte(parkXml), &parks)
    par, _ := json.Marshal(parks)
    fmt.Printf("%s
", par)
}

What i want is a generic function which takes xml string and dataStruct and returns a Json output. But below function is throwing an error How to impliment this?

func Xml2Json(xmlString string, DataStruct interface{}) (jsobj string, err error) {
    var dataStruct DataStruct
    xml.Unmarshal([]byte(personXml), &dataStruct)
    js, _ := json.Marshal(dataStruct)
    return fmt.Sprintf("%s
", js), nil
}

func main() {
    jsonstring, _ := Xml2Json(personXml, Persons)
}

Error message:

prog.go:73: DataStruct is not a type

prog.go:80: type Persons is not an expression

goplay link: http://play.golang.org/p/vayb0bawKx

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2条回答 默认 最新

  • duangu9997 2013-08-15 08:48
    已采纳

    You can not store a type (like Persons) in an interface. You could pass a reflect.Type to your function. Then, your call would look like Xml2Json(personXml, reflect.TypeOf(Persons)) which is quite ugly in my opinion.

    The better approach is probably:

    func Xml2Json(xmlString string, value interface{}) (string, error) {
        if err := xml.Unmarshal([]byte(xmlString), value); err != nil {
            return "", err
        }
        js, err := json.Marshal(value)
        if err != nil {
            return "", err
        }
        return string(js), nil
    }
    

    You can use this function with Xml2Json(personXml, new(Persons)) if you are not interested in the value itself, and

    var persons Persons
    Xml2Json(personXML, &persons)
    

    when you also want to retrieve the struct value for later processing.

    已采纳该答案
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  • doukunsan5553 2013-08-15 08:53

    The function Xml2Json declares a parameter named DataStruct. In the same scope the identifier DataStruct cannot denote a type name. If you want to use the type name DataStruct within the same scope, you must name your parameter differently.

    In the main function the problem is that a function call syntax expects an expression list within the parenthesis. There you're passing a type name, which clearly cannot be an expression.

    So to answer your question: No, you cannot pass a type as an argument to a function. But you can pass an instance of a type (in this case a pointer to such instance) to get the effect you're about:

    package main
    
    import (
            "encoding/json"
            "encoding/xml"
            "fmt"
            "log"
    )
    
    type Persons struct {
            Person []struct {
                    Name string
                    Age  int
            }
    }
    
    type Places struct {
            Place []struct {
                    Name    string
                    Country string
            }
    }
    
    type Parks struct {
            Park struct {
                    Name     []string
                    Capacity []int
            }
    }
    
    const (
            personXml = `
        <Persons>
            <Person><Name>Koti</Name><Age>30</Age></Person>
            <Person><Name>Kanna</Name><Age>29</Age></Person>
        </Persons>
    `
            placeXml = `
        <Places>
            <Place><Name>Chennai</Name><Country>India</Country></Place>
            <Place><Name>London</Name><Country>UK</Country></Place>
        </Places>
    `
    
            parkXml = `
        <Parks>
            <Park><Name>National Park</Name><Capacity>10000</Capacity></Park>
            <Park><Name>Asian Park</Name><Capacity>20000</Capacity></Park>
        </Parks>
    `
    )
    
    func Xml2Json(xmlString string, DataStruct interface{}) (jsobj string, err error) {
            if err = xml.Unmarshal([]byte(xmlString), DataStruct); err != nil {
                    return
            }
    
            js, err := json.Marshal(DataStruct)
            if err != nil {
                    return
            }
    
            return fmt.Sprintf("%s", js), nil
    }
    
    func main() {
            var p Persons
            jsonstring, err := Xml2Json(personXml, &p)
            if err != nil {
                    log.Fatal(err)
            }
    
            fmt.Println(jsonstring)
    
            var q Places
            jsonstring, err = Xml2Json(placeXml, &q)
            if err != nil {
                    log.Fatal(err)
            }
    
            fmt.Println(jsonstring)
    
            var r Parks
            jsonstring, err = Xml2Json(parkXml, &r)
            if err != nil {
                    log.Fatal(err)
            }
    
            fmt.Println(jsonstring)
    
    }
    

    Playground


    Output:

    {"Person":[{"Name":"Koti","Age":30},{"Name":"Kanna","Age":29}]}
    {"Place":[{"Name":"Chennai","Country":"India"},{"Name":"London","Country":"UK"}]}
    {"Park":{"Name":["National Park","Asian Park"],"Capacity":[10000,20000]}}
    
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